Hydrology in ArcGIS Pro, Lab Exercise 6: Creating a Flow Accumulation Raster

This lab will demonstrate the Flow Accumulation tool in ArcGIS Pro. A Flow Accumulation raster is used to calculate the size of the catchment area that drains into every point on the landscape, and is generated from the Flow Direction raster, which was in turn generated from the filled DEM. If the flow direction raster is not generated from a filled DEM, then you’ll have the same problems with your Flow Accumulation raster that you saw with your Watershed raster in Lab Exercise 2.

While these Flow Accumulation values are interesting enough in themselves, we can also use them to generate additional interesting and useful data, such as stream flow networks and a topographic wetness index. Each Flow Accumulation raster cell value will tell you the number of raster cells that drained into that cell. A value of 0 means that no cells drain into it (i.e. it is at the top of a ridge or hill). Cells that are at the exact bottom of a drainage, directly in the flow path, tend to have very high flow accumulation values, orders of magnitude larger than their neighbors, and we take advantage of these extreme differences in flow accumulation values to identify where the actual flow path is.

Basic Hydrologic Analysis in ArcGIS Pro Lecture:    • Basic Hydrologic Analysis in ArcGIS Pro  

Lab Exercises:
Lab 1: Calculating Areas from Raster Datasets;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 2: Problems when creating Watersheds without filling the DEM;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 3: Filling Sinks in a DEM;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 4: Calculating an Accurate Flow Direction Raster;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 5: Generating an Accurate Watershed;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 6: Creating a Flow Accumulation Raster;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 7: Generating a Stream Network using Strahler Stream Orders;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 8: Aspect Statistics within Watershed;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 9: Slope Statistics within Watershed;    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 10: The Topographic Wetness Index (TWI);    • Hydrology in ArcGIS Pro, Lab Exercise...  
Lab 11: Finding the Shortest Path Through the Stream Network;    • Hydrology in ArcGIS Pro, Lab Exercise...  

Extra Materials:
Word Document with walk-throughs of lab exercises: https://docs.google.com/document/d/13...

Data for Lab Exercises: https://drive.google.com/file/d/1i07m...

Manuscripts discussing TWI: https://drive.google.com/file/d/1W4Ty...